1. Field of the Invention
The present invention relates to a carbon fiber-reinforced composite material having a low specific gravity and excellent strength, heat resistance, oxidation resistance and thermal shock resistance.
2. Description of the Related Art
Since a carbon fiber-reinforced carbon composite material comprising a carbon matrix and reinforcing carbon fibers contained therein, namely a C/C composite has excellent heat resistance and strength properties at high temperatures, its application, for example, for an insulating material to be used in a space shuttle is expected and studied.
However, since the C/C composite comprises the carbon matrix, it has insufficient oxidation resistance although it has a low specific gravity and good strength properties.
To impart the oxidation resistance to the C/C composite, it is proposed to apply an oxidation resistant ceramic coating on the surface of C/C composite. However, since a difference between a coefficient of thermal expansion of the C/C composite and that of the ceramic coating is very large, the coating layer tends to be cracked due to thermal stress so that the ceramic coating is peeled off or the strength is greatly decreased.
A carbon fiber-reinforced ceramic composite material comprising a ceramic matrix and reinforcing carbon fibers contained therein, namely a C/ceramic composite has a larger coefficient of thermal expansion than the C/C composite. Therefore, when the ceramic coating is formed on the C/ceramic composite, the coating layer is not cracked due to the thermal stress and the composite has better oxidation resistance. However, the C/ceramic composite has much lower strength than the C/C composite, a large specific gravity and a large coefficient of thermal conductivity, so that the C/ceramic composite is inferior in weight reduction and heat shielding property to the C/C composite.